A chemical reaction is a chemical change which results in the formation of one or more products. The initial reactants that are taken differ in physical or chemical characteristics from the products formed. Chemical reactions generally involve either the formation or the breaking of chemical bonds.
The different types of reactions are:
Direct combination reaction also known as synthesis reaction:
In this kind of reaction two or more products combine to form one complex product.
The general form can be represented by -
A + B → AB
2Fe + 3Cl2 2FeCl3
8 Fe + S8 → 8 FeS
Decomposition reaction also known as analysis reaction:
In these kinds of reactions, one compound is broken down into two or more simpler compounds.
Its general form is -
AB → A + B
Cu(CO3) CuO + CO2
2 H2O → 2 H2 + O2
Single displacement or substitution reaction:
In these kinds of reactions one element displaces another form a compound to form a new compound and the displaced element. Generally the more reactive elements displace the less reactive element in a compound.
General form –
A + BC → AC + B
Zn + H2SO4 ZnSO4 + H2
Zn + 2 HCl → ZnCl2 + H2
Double displacement or double decomposition reaction also known as metathesis:
In these kinds of reactions the two reacting compounds exchange their radicals or ions to form two new compounds.
AB + CD → AD + CB
ZnO + 2HCl ZnCl2 +H2O
NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)
A type of double displacement reaction is an acid base reaction:
As the name suggests these kinds of reactions occur between an acid and a base. It is a neutralization reaction and is characterized by the formation of a salt and water. The hydronium (H+) ion in the acids reacts with the hydroxide (OH-) ion in the base to form these products.
General form Example –
HA + BOH → H2O + BA
HCl + NaOH NaCl + H2O
HBr + NaOH → NaBr + H2O
Redox Reaction or Oxidation – Reduction reaction:
In these kinds of reactions both oxidation and reduction take place simultaneously in the reaction. Oxidation is characterized by addition of oxygen or an electronegative element and removal of an electro positive element, while reduction is the absolute opposite of this. It involves addition of hydrogen. In general oxidation is characterized by loss of electrons while reduction is characterized by gain of electrons.
Example of redox reaction-
2 S2O32−(aq) + I2(aq) → S4O62−(aq) + 2 I−(aq)
Here I2 is reduced to I- and S2O32- is oxidized to S2O4 2-
This reaction involves water. General form is -
X-(aq) + H2O(l) ↔ HX(aq) + OH-(aq)
In these kinds or reactions the structural arrangement of a compound is becomes altered.
CH3- CH2-CH2-CH3 —> CH3